【发布时间】：2017-06-29 18:24:16
【问题描述】：
我对 play 框架以及如何将其与 Scala 一起使用是新手。我想为大 Json 对象构建一个代理。到目前为止，我实现了 json 存储在缓存中，如果它不存在，则从 web 服务请求。
但是，当有两个请求进入时，针对相同的端点（webservice 和路径相同），应该只执行一个调用，另一个请求应该等待第一个调用的结果。目前它正在对每个请求执行对服务的调用。
这是我的控制器：
@Singleton
class CmsProxyController @Inject()(val cmsService: CmsProxyService) extends Controller {
implicit def ec : ExecutionContext = play.api.libs.concurrent.Execution.defaultContext
def header(path: String) = Action.async { context =>
cmsService.head(path) map { title =>
Ok(Json.obj("title" -> title))
}
}
def teaser(path: String) = Action.async { context =>
cmsService.teaser(path) map { res =>
Ok(res).as(ContentTypes.JSON)
}
}
}
这是服务：
trait CmsProxyService {
def head(path: String): Future[String]
def teaser(path: String): Future[String]
}
@Singleton
class DefaultCmsProxyService @Inject()(cache: CacheApi, cmsCaller: CmsCaller) extends CmsProxyService {
private val BASE = "http://foo.com"
private val CMS = "bar/rest/"
private val log = Logger("application")
override def head(path: String) = {
query(url(path), "$.payload[0].title")
}
override def teaser(path: String) = {
query(url(path), "$.payload[0].content.teaserText")
}
private def url(path: String) = s"${BASE}/${CMS}/${path}"
private def query(url: String, jsonPath: String): Future[String] = {
val key = s"${url}?${jsonPath}"
val payload = findInCache(key)
if (payload.isDefined) {
log.debug("found payload in cache")
Future.successful(payload.get)
} else {
val queried = parse(fetch(url)) map { json =>
JSONPath.query(jsonPath, json).as[String]
}
queried.onComplete(value => saveInCache(key, value.get))
queried
}
}
private def parse(fetched: Future[String]): Future[JsValue] = {
fetched map { jsonString =>
Json.parse(jsonString)
}
}
//retrieve the requested value from the cache or from ws
private def fetch(url: String): Future[String] = {
val body = findInCache(url)
if (body.isDefined) {
log.debug("found body in cache")
Future.successful(body.get)
} else {
cmsCaller.call(url)
}
}
private def findInCache(key: String): Option[String] = cache.get(key)
private def saveInCache(key: String, value: String, duration: FiniteDuration = 5.minutes) = cache.set(key, value, 5.minutes)
}
最后是对网络服务的调用：
trait CmsCaller {
def call(url: String): Future[String]
}
@Singleton
class DefaultCmsCaller @Inject()(wsClient: WSClient) extends CmsCaller {
import scala.concurrent.ExecutionContext.Implicits.global
//keep those futures which are currently requested
private val calls: Map[String, Future[String]] = TrieMap()
private val log = Logger("application")
override def call(url: String): Future[String] = {
if(calls.contains(url)) {
Future.successful("ok")
}else {
val f = doCall(url)
calls put(url, f)
f
}
}
//do the final call
private def doCall(url: String): Future[String] = {
val request = ws(url)
val response = request.get()
val mapped = mapResponse(response)
mapped.onComplete(_ => cmsCalls.remove(url))
mapped
}
private def ws(url: String): WSRequest = wsClient.url(url)
//currently executed with every request
private def mapResponse(f: Future[WSResponse]): Future[String] = {
f.onComplete(_ => log.debug("call completed"))
f map {res =>
val status = res.status
log.debug(s"ws called, response status: ${status}")
if (status == 200) {
res.body
} else {
""
}
}
}
}
我的问题是：如何只执行一次对 web 服务的调用？即使对同一个目标有多个请求。我不想阻止它，其他请求（不确定我在这里是否使用了正确的词）只会被告知已经有一个 web 服务调用在路上。
header 和 teaser 的请求，见控制器，应该只对 web 服务执行一次调用。
【问题讨论】：
标签： json scala web-services playframework future